We’ve noticed a significant increase in the incidence and severity of foliar blotches in some apple blocks this summer. Most of these have been Alternaria Leaf Blotch, but there have been a few instances of Necrotic Leaf Blotch as well. While one of these is a disease and the other a physiological disorder, both require a period of heat followed by a period of wetness and/or high humidity. These are conditions we create with overhead cooling – we’re cooling because of the heat and doing so of course increases humidity and a prolonged period of leaf wetness. While we’ve successfully used overhead cooling for years, this year we’ve started earlier and cooled practically every day for 8 – 10 weeks now, resulting in optimum conditions for ALB and NLB. One thing this does is to illustrate the importance of good water management, especially for overhead cooling. The attached document goes into further detail about what we’ve been seeing and some possible management options.
Byron Phillips, Wilbur-Ellis Key Account Manager